Lateral steering control is an important feature in projectile guidance systems. Such control provides the ability to improve weapon accuracy and correct for initial aiming errors and target maneuvers.
Various lateral projectile control techniques are known in the art. One of such techniques is based on aerodynamic control, and include deflecting tail fins, canard lifting surfaces and other deflecting elements.
Another known technique is based on jet thrust control and include cold gas jet thrusters, warm gas jet thrusters, impulse thrusters and explosive thrusters. These systems, for example, can employ side mounted exhaust outlets coupled to sources of highly pressurized gases through adjustable control valves. In the case of self-propelled missile, such sources are usually common to the fuel source of the missile. Whilst, in the case of fired projectiles, the sources dedicated to the steering function are separately ignited by an auxiliary device.
For example, U.S. Pat. Nos. 4,726,544 and 5,044,156 describe various steering systems for the final phase of a guided projectile. The steering is achieved by control jets acted upon by hot gas created in a combustion chamber.
U.S. Pat. No. 4,573,648 teaches the use of ram air for thermodynamic ignition of a solid fuel. The steering system includes an open-ended diffusion chamber and an adjacent combustion chamber located in the nose of a projectile to receive ram air that ignites a solid fuel material within the combustion chamber. A pair of oppositely disposed lateral steering ports are provided aft of the combustion chamber and are interconnected therewith via a diverting valve that is controllable to selectively divert the escaping combustion gases from the combustion chamber to one or both of the steering ports to thereby change or maintain the trajectory course of the projectile after firing.
The systems which are dependent upon a propellant source carried onboard the missiles and/or projectiles face problems related to fuel exhaustion and shift in center of mass as fuel is used. These systems may also introduce the additional complexity associated with combustion chamber and fuel supply systems.
The use of rain air for lateral steering control instead of the gas created in a combustion chamber is also known in the art (see, for example, U.S. Pat. Nos. 4,522,357, 4,685,639 and 4,537,371).
For example, U.S. Pat. No. 4,522,357 teaches the use of ram air for steering a projectile which is fin stabilized and has a normal in-flight roll rate of about 1200 rpm. The ram air enters a nose opening in a projectile during projectile flight passes to a central chamber and is selectively diverted to laterally positioned and oppositely oriented steering jets. The steering jets are interconnected with the aft end of the central chamber. A diverting mechanism is located between the central chamber and each of the steering jets to allow either one or none of the steering jets to provide correctional steering forces when desired. The diverting mechanism includes a deflector mounted on a shaft and rotated in the opposite direction to that of the rotating projectile. In order to provide a differently directed thrust force, the deflector is rotationally driven at a different speed so that the steering thrust vector is redirected. The projectile is guided to the target via an information beam of energy radiated from a source at the firing location. The information beam contains relative location codes which are used together with vertical reference information derived from on-board roll reference sensor to correct the flight path of the projectile.
U.S. Pat. No. 4,537,371 describes a small caliber guided projectile having a forward opening inlet which provides supersonic stream ram air to a flow control mechanism prior to exhausting such air through a pair of diametrically opposed bifurcated guidance nozzles. The flow control mechanism includes a primary flow passageway and orifice switching devices for controlling bypass flow to the exhaust nozzles. Means of vortex generation is located upstream of the discharge of the flow through switching devices into the nozzles. When the switching devices are closed, flow over the means of vortex generation generates a small vortex for triggering a boundary attachment flow as a result of the Coanda effect and increases flow through the nozzle. Opening of the orifice switching device results in aspiration through the nozzle, thereby impeding flow. By controlling the respective switching devices, flow through the opposed nozzles may be varied to produce a resultant lateral force on the projectile, permitting control of the trajectory of the projectile.